This invention concerns a composite primary backing for use in the preparation of tufted carpets having low static propensity and attractive coloration. Considerable research has been done in the past to develop carpets which are free from annoying spark discharge. The discharge occurs when a person who has walked over the carpet touches a grounded surface, thereby releasing electrostatic charges collected from the carpet. One method for avoiding the development of electrostatic charges in carpets has been to use pile yarns containing a small percentage of conductive fibers such as copper, stainless steel, metal-plated fibers or carbon-filled organic polymeric filaments. Methods of this type are described in U.S. Pat. Nos. 3,582,444; 3,582,445; 3,288,175; 2,764,185; British Pat. No. 1,216,5l5; and French Pat. No. 1,567,529 (Example 1). While this conductive pile approach has been useful in loop pile carpets it has not been very effective in cut pile carpets.
Another approach has been to use conductive materials in latex applied to the lower surface of the backing, as for example in U.S. Pat. No. 3,510,386 and French Pat. No. 1,567,536. While this latex method is useful when the pile fibers are conductive it is less effective when the pile fibers are nonconductive. In U.S. Pat. No. 2,302,003, a method has been described which utilizes conductive latex as a coating for some of the pile tufts and also as a coating for the entire back side of the carpet. The latex is made conductive by incorporating conductive carbon. This method is not completely adequate, for the conductive carbon tends to wick up into the pile causing dark spots to show through the pile. In addition when a secondary backing is glued to the bottom surface of the primary backing, the conductive carbon runs through the secondary backing making it unattractive.
Another solution lies in use of stainless steel fibers in both backing and in pile as in U.S. Pat. No. 3,288,175, but the cost is excessive for carpets destined for ordinary home use. Also experience has shown that conductivity of carpets containing metallic fibers tends to decrease with continuing use, possibly through loss of the fiber from the carpet.
Aside from the work which has been done to make tufted carpets antistatic, considerable work has been done on floor mats which are used in the untufted state. These mats are dense and very thick and cannot be used for tufting because of needle breakage or destruction of the carpet backing during tufting. French Pat. Nos. 1,567,529 and 1,567,536 describe mats of this type.